The science behind guitars

Frequency response of Parlour 6

When I began building guitars I had very little idea how they actually worked, so I set about doing a whole series of experiments to try to get answers to some of my many questions. I learned a lot, and I picked up bits and pieces of useful information from reading in books and on the web as well.

Still, there were so many different ideas and assertions, often conflicting, that it was hard to know what to believe and what to reject.

For example, I was very attracted to the idea of tap tuning put forward by Roger H Siminoff (The Art of Tap Tuning, Siminoff, Hal Leonard, USA 2006). He maintains that the sound of a guitar can be altered and set, before gluing the top on, by tapping each top brace and trimming it to ring at a particular frequency.

When you try to do it, it doesn’t take long to find out that a guitar top actually vibrates as a whole piece. While you can certainly make it vibrate differently as a whole by trimming one or more braces, tapping any one brace gives the same frequency as tapping any other brace. Changing one changes all.

Moreover, after being attached to the rest of the soundbox, the top vibrates completely differently than it did before. A nice idea, but an example of a sincerely-held belief that has no basis in fact.

I still use tap tuning, but very differently now. A fellow luthier (John Buckham from Wauchope) put me onto a book by Trevor Gore and Gerard Gilet that I think contains the finest research into the physics and structure of high performing guitars in the world. (Contemporary Acoustic Guitar, Gore and Gilet, Everbest Printing, Australia 2011)

Gore is a physicist and loves his differential equations, but the two volumes are written in a very accessible style and you can skip the maths without any problems. And I’ve learned that a single tap gives an incredible window into the total response of a guitar – here’s a picture of my mighty tap hammer. It produced the image at the top of this page, which is the frequency response of my latest Parlour 6. Well, I helped.

I intend to go into the physics in much more detail in my blog pages, if you’re interested.